Up to now, carbon black has been used as a reinforcing filler for rubbers such as tires. This is because carbon black has higher reinforcing ability and abrasion resistance as compared to other fillers. The microstructurization of carbon black is known to be effective in enhancing the abrasion resistance and tear resistance of heavy-duty tires for rough roads. Carbon black aggregates with narrow size distribution are known to exhibit substantially enhanced reinforcing ability.
On the other hand, a method of producing a readily processable rubber is known to use a wet masterbatch. The method is as follows: a slurry is prepared in such a manner that water is mixed with a filler such as carbon black or silica at a predetermined ratio in advance and the filler is finely dispersed in water with mechanical force; the slurry and a rubber latex are mixed together; the mixture is coagulated by adding a coagulant such as an acid, an inorganic salt, or an amine to the mixture; and the coagulate is recovered and then dried.
The following masterbatches have been recently reported (Patent Documents 1 and 2): natural rubber masterbatches which do not have problems inherent to natural rubber wet masterbatches containing natural rubber, carbon black, silica, another inorganic filler, and the like, that is, problems that the natural rubber wet masterbatches have a less improvement in processability as compared to wet masterbatches containing synthetic rubber and therefore it is difficult to uniformly disperse such fillers but which have high processability, reinforcing ability, and abrasion resistance.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2003-41055 (Claims and the like)    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2004-99625 (Claims and the like)